Desaturase

ABSTRACT

This invention relates to cDNA sequences encoding Δ5-fatty acid desaturases comprising the sequences shown in SEQ.1 and SEQ.2.

[0001] This invention relates to DNA sequences encoding Δ5-fatty acid desaturases, the encoded Δ5-fatty acid desaturases, and applications for the Δ5-fatty acid desaturases.

[0002] Polyunsaturated fatty acids are important neutraceutically due to their specific health promoting activities, and biomedically in respect of their potential pharmaceutical applications in the treatment of specific disease conditions.

[0003] Polyunsaturated fatty acids are the precursors for two major classes of metabolites: prostanoids (which include prostaglandins and thromboxanes) and leukotrienes. Δ5-fatty acid desaturase catalyses the conversion of dihomogammna linolenic acid (DHL) to arachidonic (AA) acid, and eicosatetraenoate (ETA) to ecosapentaenoate (EPA), by the introduction of double bonds at the Δ5 carbon of the respective substrates, and exists as an endoplasmic reticulum membrane-bound protein in its native state.

[0004] Arachidonic acid has a 20 carbon chain with 4 double bonds and is of great importance in human metabolism since it is a precursor for the synthesis of prostaglandins—20-carbon chain fatty acids that contain a 5 carbon ring. Prostaglandins are modulators of hormone action and the potential effects of prostaglandins include the stimulation of inflammation, the regulation of blood flow to particular organs, the control of ion transport across some membranes, and the modulation of synaptic transmission. Prostaglandins are also potentially useful as contraceptives due to their ability to suppress progesterone secretion. Therefore, the ability to modulate prostaglandin synthesis by controlled levels of expression of polyunsaturated fatty acid precursor synthesis is very important both medically and commercially.

[0005] The increased importance of polyunsaturated fatty acids in the food and pharmaceutical industries has led to an increased demand which has exceeded current production levels and supplementary sources of high quality, low cost polyunsaturated fatty acids are required.

[0006] Current commercial sources of polyunsaturated fatty acids include selected seed plants, marine fish and selected mammals, and traditional processing techniques for extracting the polyunsaturated fatty acids from these sources include solvent extraction, winterization, urea-adduct formation and distillation. However, present sources have the disadvantages of seasonal and climatic variations in both production levels and quality, a lack of availability of plant and fish sources, and the high costs of refining low-grade oils. High costs coupled with insufficient production levels have retarded the development of commercially exploitable applications of polyunsaturated fatty acids.

[0007] Much effort has gone into developing alternative sources of polyunsaturated fatty acids, and studies have been carried out to characterise the constituent genes and encoded proteins of their biosynthesis. The engineering of polyunsaturated fatty acid biosynthesis into oilseeds for example has many advantages for the production of large scale quantities of, for example, γ-linolenate (GLA), dihomo-γ(-linolenate (DHGLA), arachidonic acid (AA), eicosapentaenoate (EPA) and docosahezaenoate (DHA). The practicality of this has been illustrated by the expression of a Borage Δ6 desaturase gene in tobacco resulting in the production of GLA and the octadecatetraenoic acid, 18:4 (Soyanova et al (1997), PNAS 94, 9411-9414). As more of the biosynthetic genes for polyunsaturated fatty acid synthesis become available, this opens up the possibility of producing at least GLA, AA, EPA and DHA in oil seeds, as well as controlling the type of lipid assembled. Benefits which would be obtained from such crops include a cheap and sustainable supply of desirable polyunsaturated fatty acids on a large scale, tailored polyunsaturated fatty acids profiles to meet specific nutritional requirements, and in the fine chemical industry, the production of unusual fatty acids with prescribed levels and locations of unsaturation.

[0008] A further approach to the production of polyunsaturated fatty acids is to utilise the biosynthetic capacity of lower organisms e.g. algae, bacteria, fungi (including phycomycetes) which can synthesise the entire range of polyunsaturated fatty acids and can be grown on an industrial scale. Genetic transformation of these organisms will enable the development of overproducing strains and the manipulation of the polyunsaturated profile by pathway engineering.

[0009] Fungal Δ5 and Δ6 fatty acid desaturases have been cloned, and their sequences disclosed in WO98/46763, WO98/46764 and WO98/46765.

[0010] Polyunsaturated fatty acid metabolism is of greatest importance in human metabolism. These acids, via the eicosanoids, are fundamental to the proper maintenance of homeostasis and are linked to serious physiological and pathophysiological syndromes.

[0011] The inventors have surprisingly isolated and characterised a DNA sequence from the soil-borne filamentous fungus of the zygomycete class Mortierella alpina encoding a functional Δ5-fatty acid desaturase.

[0012] In addition, the inventors have surprisingly isolated and characterised a DNA sequence from the nematode worm, Caenorhabditis elegans encoding a functional Δ5-fatty acid desaturase. This DNA sequence, encoding a functional Δ5-fatty acid desaturase is thought likely to be more closely related to the human Δ5-fatty acid desaturase than any of the Δ5-fatty acid desaturase gene sequences isolated so far.

[0013] As well as the potential human benefits from the polypeptide encoded by the DNA sequences of this invention, the DNA sequences of this invention may enable the cloning of the equivalent human gene and thereby facilitate overproduction of the human DNA sequence and allow its biomedical exploitation in the treatment of certain human diseases.

[0014] Plant and fungal desaturases are mainly integral membrane polypeptides which makes them difficult to purify and subsequently characterise by conventional methods. Hence, molecular techniques including the use of mutants and transgenic plants have been adopted in order to better study lipid metabolism.

[0015] A first aspect of the invention provides an isolated animal Δ5-fatty acid desaturase and functional portions thereof.

[0016] A second aspect of the invention provides an isolated C. elegans Δ5-fatty acid desaturase.

[0017] A third aspect of the invention provides a DNA sequence according to a first or second aspect of the invention comprises at least a portion of the sequence shown in SEQ.2 and equivalents to that sequence, or to portions of that sequence, which encode a functional Δ5-fatty acid desaturase by virtue of the degeneracy of the genetic code. Preferably, the DNA sequence is derived from a Caenorhabditis elegans DNA sequence.

[0018] Preferably, the gene encoding the Δ5-fatty acid desaturase encoded by the cloned gene is 1341 bp long. The protein is 447 amino acids long with an estimated molecular weight of 57 kDa.

[0019] Alternatively, the DNA sequence encodes a functional Δ5-fatty acid desaturase and comprises at least a portion of the sequence shown in SEQ.1 and equivalents to that sequence, or to portions of that sequence, which encode a functional Δ5-fatty acid desaturase by virtue of the degeneracy of the genetic code. Preferably, the DNA sequence is derived from a Mortierella alpina DNA sequence.

[0020] Preferably, the gene encoding the Δ5-fatty acid desaturase encoded by the cloned gene is 1338 bp long. The protein is 446 amino acids long with an estimated molecular weight of 57 kDa.

[0021] Preferably, a DNA sequence according to a third aspect of the invention is functional in a mammal.

[0022] Preferably, the DNA sequence is expressed in a mammal.

[0023] Preferably, the DNA sequence is expressed in a human.

[0024] Preferably, the DNA sequence is obtained by modification of a functional natural gene encoding a Δ-5 fatty acid desaturase.

[0025] Preferably, the modification includes modification by chemical, physical, or biological means without removing a catalytic activity of the enzyme which it encodes.

[0026] Preferably, the modification improves a catalytic activity of the enzyme which it encodes.

[0027] Preferably, the biological modification includes recombinant DNA methods and forced evolution techniques.

[0028] Preferably, the forced evolution technique is DNA shuffling.

[0029] A fourth aspect of the invention provides a polypeptide encoded by a DNA sequence according to a third aspect of the invention.

[0030] Preferably, at least a portion of the polypeptide has the sequence shown in SEQ.3 or functional equivalents to that sequence or portions of that sequence. Alternatively, at least a portion of the polypeptide has the sequence shown in SEQ.4 or functional equivalents to that sequence or portions of that sequence.

[0031] Preferably, the polypeptide catalyses the conversion of dihomogamma linolenic acid to arachidonic acid.

[0032] Preferably, the polypeptide has been modified without removing the catalytic activity of the encoded polypeptide.

[0033] Preferably, the polypeptide has been modified in such a way as to introduce a specific level of saturation of a substrate at a specific location within the molecular structure of the substrate.

[0034] A fifth aspect of the invention provides a vector containing a DNA sequence of any portion of a DNA sequence according to a third aspect of the invention..

[0035] A sixth aspect of the invention provides a method of producing polyunsaturated fatty acids comprising contacting a substrate with a Δ5-fatty acid desaturase according to a first or second aspect of the invention, or a polypeptide according to a fourth aspect of the invention.

[0036] A seventh aspect of the invention provides a method of converting dihomogamma linoleic acid to arachidonic acid wherein the conversion is catalysed by a Δ5-fatty acid desaturase according to a first or second aspect of the invention, or a polypeptide according to a fourth aspect of the invention.

[0037] An eighth aspect of the invention provides an organism engineered to produce high levels of a polypeptide according to a fourth aspect of the invention.

[0038] A ninth aspect of the invention provides an organism engineered to produce high levels of a product of a reaction catalysed by a Δ5-fatty acid desaturase according to a first or second aspect of the invention, or by a polypeptide according to a fourth aspect of the invention.

[0039] Preferably, the organism has been engineered to carry out the method according to a sixth or seventh aspect of the invention.

[0040] Preferably, the organism is a microorganism.

[0041] Preferably, the microorganism is selected from algae, bacteria and fungi.

[0042] Preferably, the fungi includes phycomycetes. Alternatively, the microorganism is a yeast.

[0043] Alternatively, the organism is a plant. Preferably, the plant is selected from oil seed plants.

[0044] Preferably, the oil seed plants are selected from oil seed rape, sunflower, cereals including maize, tobacco, legumes including peanut and soybean, safflower, oil palm, coconut and other palms, cotton, sesame, mustard, linseed, castor, borage and evening primrose.

[0045] A tenth aspect of the invention provides a seed or other reproductive material derived from an organism according to a ninth aspect of the invention.

[0046] Preferably, the organism is a mammal.

[0047] An eleventh aspect of the invention provides an isolated multienzyme pathway wherein the pathway includes a Δ5-fatty acid desaturase according to a first or second aspect of the invention.

[0048] A twelfth aspect of the invention provides a compound produced by a conversion of a substrate, wherein said conversion is catalysed by a Δ5-fatty acid desaturase according to a first or second aspect of the invention.

[0049] A thirteenth aspect of the invention provides an intermediate compound produced by the reaction catalysed by a Δ5-fatty acid desaturase according to a first or second aspect of the invention.

[0050] A fourteenth aspect of the invention provides a foodstuff or dietary supplement containing a polyunsaturated fatty acid produced by a method according to a sixth aspect of the invention.

[0051] A fifteenth aspect of the invention provides a pharmaceutical preparation containing a polyunsaturated fatty acid produced by a method according to a sixth aspect of the invention.

[0052] A sixteenth aspect of the invention provides prostaglandins synthesised by a biosynthetic pathway including a catalytic activity of a Δ5-fatty acid desaturase according to a first or second aspect of the invention.

[0053] A seventeenth aspect of the invention provides a method for the modulation of prostaglandins synthesis by the control of the levels of expression of a DNA sequence according to a third aspect of the invention.

[0054] An eighteenth aspect of the invention provides a probe comprising all or part of a DNA sequence according to a third aspect of the invention,or an equivalent RNA sequence.

[0055] A nineteenth aspect of the invention provides a probe comprising all or part of a Δ5-fatty acid desaturase polypeptide according to a fourth aspect of the invention.

[0056] A twentieth aspect of the invention provides a method of isolating Δ5-fatty acid desaturases using a probe according to a nineteenth aspect of the invention.

[0057] It is possible that the gene of the invention may be transformed into human cells and exploited in gene therapy techniques at a suitable level in vivo to provide a constant supply of enzyme converting fatty acids to polyunsaturated fatty acids within the patient's body. This could be an effective preventative treatment for example, in patients suffering high levels of cholesterol or other medical conditions where administration of polyunsaturated fatty acids may have beneficial disease-preventative effects.

[0058] In addition, either whole or part of the DNA sequences of the invention, or whole or part of the polypeptide sequences of the invention could be used as search probes for research or diagnostic purposes.

[0059] The invention will now be described by way of example only, with reference to the accompanying drawings, SEQ.1 to SEQ.4, and FIGS. 1 to 4, in which:

[0060] SEQ.1 is a cDNA sequence encoding Δ5-fatty acid desaturase from Mortierella alpina and;

[0061] SEQ.2 is a cDNA sequence encoding Δ5-fatty acid desaturase from C. elegans ; and

[0062] SEQ.3 is the peptide sequence obtained by translating the gene sequence of SEQ.1; and

[0063] SEQ.4 is the peptide sequence obtained by translating the gene sequence of SEQ2; and

[0064]FIG. 1 is a line-up of the gene encoding Mortierella alpina Δ5-fatty acid desaturase with various Δ6 desaturases and a Δ12 desaturase; and

[0065]FIG. 2 is a line-up of the gene encoding Δ5-fatty acid desaturase with the C. elegans Δ6 desaturase and the fungal Δ5 desaturase from M. alpina; and

[0066]FIG. 3 is a gas chromatography trace of the fatty acid methyl esters of induced yeast cell transformants transformed with the Mortierella alpina Δ5-fatty acid desaturase gene and uninduced yeast cell transformants; and

[0067]FIG. 4 is a gas chromatography trace of the fatty acid methyl esters of induced yeast cell transformants transformed with the C. elegans Δ5-fatty acid desaturase gene and uninduced yeast cell transformants.

[0068] Cloning and Sequencing of the Δ5-Fatty Acid Desaturase Gene from Mortierella alpina

[0069] The DNA sequences of the invention encode Δ5-fatty acid desaturases and were cloned using PCR technology in combination with cDNA library templates and specifically designed primers. The function of the DNA sequences, namely the conversion of dihanogamma linolenic acid (DHL) to arachidonic acid (AA), and eicostatetraenoate (ETA) to ecosapentaenoate (EPA), were verified by expressing the corresponding cDNAs in yeast.

[0070] The Δ5-fatty acid desaturase gene from Mortierella alpina was cloned by Polymerase Chain Reaction (PCR) techniques using cDNA from Mortierella alpina as the template and specifically designed degenerate oligonucleotide primers (DP) as shown below, based on the first and third histidine bases of plant Δ12 and Δ15 desaturases previously identified by Shanklin (Shanklin, J, Whittle, E J & Fox, B G. Biochemistry. 33, 12787-12794 (1994)). ps Degenerate Oligonucleotide Primers (DP) 5′-GCGAATTA(A/T)TIGGICA(T/C)GA(T/C)TG(T/C)GICA-3′ 5′-GCGAATTCATIT(G/T)IGG(A/G)AAIA(G/A)(A/G)TG(A/G)T G-3′

[0071] where I represents inosine, and the Eco RI sites are underlined.

[0072] The PCR amplifications were run entirely conventionally on a thermal cycler made by using a program of 2 minutes at 94° C. then 45 seconds at 94° C., 1 minute at 55° C. and 1 minute at 72° C. for 32 cycles followed by extension at 72° C. for a further 10 minutes. PCR amplification products were separated on 1% agarose gels.

[0073] The range of PCR products amplified from the Mortierella alpina cDNA template included a 660 bp product which was gel purified, cloned into pGEM-T (Promega®) and transformed into the Escherichia coli expression host, DH5α.

[0074] Primers (P) were designed against the 660 bp product sequence and fragment amplification carried out by PCR using the cloned 660 bp fragment as a template, and sequence-specific primers (P) based on the 660 bp product sequence. Delta B for 5′-GATGCGTCTCACTTTTCA-3′ Delta B rev. 5′-GTGGTGCACAGCCTGGTAGTT-3′

[0075] The products of this PCR amplification were gel purified and used as probes to screen a Mortierella alpina cDNA library. The fragment probe hybridised to 25 out of the 3.5×10⁵ phage clones screened and one clone was shown, by restriction analysis, to have the expected size of 1.5 kb. This clone, designated L11, was selected for further analysis.

[0076] Sequence analysis of L11 revealed an open reading frame of 1,338 bp in length encoding a polypeptide of 446 amino acids. When analyzed on the protein and genomic databases using the GCG 8 Program (Devereux J. et al. Nucleic Acids. Res.. 12, 387-395 (1984)), L11 showed a low level 20% identity to the Δ6 desaturase gene from Synechocystis sp. PCC6803 (FIG. 1).

[0077] In FIG. 1, the sequences in the line-up have the following Accession numbers: S54259 Δ12 Spirulina Accession number: X86736 S54809 Δ6 Spirulina Accession number: X87094 S68358 Putative Sphingolipid desaturase Accession number: X87143 S35157 Δ6 Synechocystis Accession number: L11421 PBOR6 Δ6 Borage Accession number U79010 FU2 Δ5 desaturase Accession number AF054824

[0078] In addition, although all three histidine boxes characteristic of desaturase enzymes are present in the translated sequence, the third histidine box located at position 1159 bp in the sequence contains the variant QXXHH. The translated sequence also contains a cytochromc b₅-like heme-binding domain at the N-terminus which includes the EHPGG motif whereas previously, this feature has only been observed at the C-terminus of other fungal desaturases.

[0079] Southern Blotting of Genomic DNA

[0080] Sequence specific primers (P) designed against the L11 sequence between histidine boxes 1 and 3 of L11, were used in a PCR reaction to amplify a 660 bp region of the L11 sequence.

[0081] The 660 bp PCR product was gel purified and Southern blots of restricted Mortierella alpina and Mucor circinelloides genomic DNA carried out using the 660 bp fragment as a probe. The results suggest that the gene encoding the Δ5-fatty acid desaturase of the invention is present in single copy in Mortierella alpina and appears to be absent from Mucor circinelloides. In addition, there is no detectable Δ5-fatty acid desaturase activity in Mucor circinelloides.

[0082] Expression of the Cloned Mortierella alpina Gene Encoding Δ5-Fatty Acid Desaturase

[0083] In order to confirm that the L11 sequence encoded a Δ5-fatty acid desaturase enzyme, the cDNA was subcloned into the yeast expression vector, pYES2, supplied by Invitrogen™ under the control of the GAL4 polymerase promoter to yield plasmid pYES2/L11. The expression of L11 was checked by in vitro transcription-translation of pYES2/L11 using the Promega™ coupled Transcription and Translation system. ³⁵S methionine-labelled translation products were generated which were run on SDS PAGE and visualised by exposure to autoradiograph film. The estimated molecular weight of the product was 55-60 kD and a control plasmid, pYES2 with no insert, failed to yield any labelled translation product.

[0084] Construct, pYES2/L11, was transformed into yeast Saccharomyces cerevisiae and grown on uracil-deficient YCA medium. Transformants were selected by virtue of the presence of the URA3 selectable marker carried by pYES2/L11 and expression of L11 was induced by the addition of galactose to a final concentration of 1% mM. The cultures were grown overnight in the presence of 0.5 mM dihomo gamma linolenate, detergent (1% tergitol NP-40) and 2% raffinose. Aliquots were harvested at t=0, t=4 hours, and t=16 hours.

[0085] Yeast total fatty acids were analysed by GC of methyl esters. The lipids from the induced and uninduced control samples were transmethylated with 1M HCL in methanol at 80° C. for 1 hr. Fatty acid methyl esters (FAMES) were extracted in hexane. GC analysis of FAMES was conducted using a Hewlett Packard 58804 Series Gas Chromatograph equipped with a 25M×0.32 mm RSL-500 BP bonded capillary column and a flame ionization detector.

[0086] When methyl esters of the total fatty acids isolated from yeast carrying the plasmid pYes2/L11 and grown in the presence of galactose and dihomo gamma linolenic acid were analysed by GC an additional peak was observed (see FIG. 3). This extra peak had the same retention time as the authentic arachidonic acid standard (Sigma) indicating that the transgenic yeast were capable of desaturating Dihomo gamma linolenic acid at the Δ5 position. No such peaks were observed in any of the control samples (transformation with pYes2) FIG. 3. The identity of the additional peak was confirmed by GCMS (Kratos MS80RFA operating at an ionization voltage of 70 eV with a scan range of 500-40 daltons) which positively identified this compound as arachidonic acid.

[0087] This demonstrates that the DNA sequence from Mortierella alpina encodes a functional polypeptide involved in the synthesis of arachidonic acid in the presence of galactose and dihomo gamma linolenate.

[0088] Cloning and Sequencing of the C. elegans Δ5-Fatty Acid Desaturase Gene

[0089] Previously, the inventors identified fungal Δ5 and Δ6-fatty acid desaturases from both plant and animal species which were distinct from previously identified microsomal desaturases. This difference was due to the presence of an N-terminal extension which showed homology to the electron donor protein cytochrome b₅.

[0090] During the characterisation of the fungal (Mortierella alpina) Δ5-fatty acid desaturase and the C. elegans Δ6-fatty acid desaturase (present on cosmid W08D2 (Accession No. Z70271)), the inventors identified a related sequence on cosmid T13F2.1 (Accession No. Z81122) also containing C. elegans DNA likely to encode a fatty acid desaturase.

[0091] Analysis of the sequences (using Genefinder program (Wilson, R. et al (1994) Nature, 368, 32-38)) revealed that cosmids W08D2 and T13F2 contained overlapping regions. In addition, it was found that cosmid T13F2 contained an open reading frame (ORF), designated T13F2.1, which contained an N-terminal cytochrome b₅ domain (defined by the diagnostic His-Pro-Gly-Gly motif), as well as three ‘histidine boxes’ characteristic of all microsomal desaturases. Further, this putative desaturase contained a variant third histidine box, with a H→Q substitution for the first histidine in the His-X-X-His-His motif. This glutamate substitution is present in both plant and animal Δ6-fatty acid desaturases and in the fungal Δ5-fatty acid desaturase from M. alpina.

[0092] The overlap between cosmids T13F2 and W08D2 allowed the determination of the proximity of the putative desaturase ORF, T13F2.1, to the Δ6-fatty acid desaturase, revealing that the two sequences were arranged in tandem on chromosome IV, separated by 990 bases from the predicted stop codon of T13F2.1 to the initiating methionine triplet of the Δ6-fatty acid desaturase.

[0093] Since sequence analysis predicted that the T13F2.1 ORF was interspersed with a number of introns, heterologous functional expression of genomic DNA was unfeasible. Therefore, the polymerase chain reaction (PCR) was used to amplify a partial cDNA clone corresponding to a large predicted exon at the 5′ end of the T13F2.1 ORF using the following primers, CEFOR AND CEREV: CEFOR: 5′- ATGGTATTACGAGAGCAAGA-3′ CEREV: 5′-TCTGGGATCTCTGGTTCTTG-3′

[0094] After initial denaturation at 94° C. for 2 minutes, amplification was performed in 32 cycles of: 45 seconds at 94° C., 1 minute at 55° C., and 1 minute at 72° C. followed by a final extension at 72° C. for a further 10 minutes.

[0095] A DNA fragment of the correct predicted size was amplified (as visualised on a 1% agarose gel), the gel band was cut out, the DNA purified and ligated directly into pGEM-T (Promega), and the resulting plasmid transformed into E. coli DH5α cells. Plasmid DNA was purified for sequencing using the Qiagen QIAprep miniprep kit, and the nucleotide sequence of the insert determined by automated sequencing using an ABI-377 DNA sequencer.

[0096] In order to isolate the complete coding region corresponding to ORF T13F2.1, this isolated 233 bp PCR-amplified fragment was used to screen a mixed stage C. elegans cDNA library that had been constructed in λZapII by Prof Yuji Kohara—Mishima, Japan. The screening was carried out using standard techniques (Sambrook et al (1989) Molecular Cloning. A Laboratory Manual) using the cloned PCR product as a probe. The DNA fragments were labelled with α [³²P] d CTP using the Ready to Go DNA-Labelling reaction mix (Pharmacia). Of 1.4×10⁵ pfu screened for hybridization to the 233 bp fragment, 5 plaques gave positive signals and were cored out of the agar plates and eluted into SM buffer. The resultant phage suspensions were screened for the presence of T13F2.1 by PCR amplification using CEFOR and CEREV. One clone, designated L4, was purified by 2 additional rounds of plating and hybridisation screening at 65° C. using the 233 bp fragment isolated by PCR. Plasmid L4 was released from λ clone L4 by excision and the cDNA insert sequenced on both strands using a Perkin Elmer AB1-377 DNA sequencer.

[0097] The resulting DNA sequence is shown in SEQ.2, and the predicted amino acid sequence is shown in SEQ.4.

[0098] Functional Analysis of L4 in Yeast

[0099] The complete coding region (coding for 447 amino acids) of L4 was amplified by PCR using the primers YCEDFor and TCEDRev shown below, which also introduced flanking HindIII and BamHI restriction sites:

[0100] YCEDFor:

[0101] 5′-GCGAAGCTTAAAATGGTATTACGAGAGCAAGAGC-3′

[0102] (annealing to the initiating methionine is indicated by the bold type face and the Hind III restriction site is underlined)

[0103] YCEDRev:

[0104] 5′-GCGGATCCAATCTAGGCAATCTTTTAGTCAA-3′

[0105] The amplified PCR product containing the complete coding region of L4 was ligated into the yeast expression vector, pYES2 (Invitrogen), downstream of the GAL1 promoter using HindIII and BamIII restriction sites (enzymes supplied by Boehringer Mannheim). The resulting construct, designated pYES2/L4, was transformed into E. coli, and the fidelity of the PCR-generated insert in plasmid pYES2/L4 was confirmed in vitro by coupled transcription/translation using the TNT system (Promega). The resulting translation products were labelled with ³⁵S methionine, separated by SDS-PAGE and visualised by autoradiography.

[0106] The translation product obtained from pYES2/L4 had a molecular weight of approximately M_(r)57,000, whereas the control vector, pYES2 with no insert, did not yield a translation product.

[0107] For functional analysis of the L4 coding region the recombinant plasmid was transformed into S. cerevisiae DBY746 by the lithium acetate method (Elble R. (1992) Bio Techniques 13 18-20). Cells were cultured overnight in a medium containing raffinose as a carbon source, and supplemented by the addition of either linoleic acid (18:2 Δ^(9,12)) or di-homo-γ-linolenic acid (C20:3 Δ^(8,11,14)) in the presence of 1% tergitol (as described by Napier et al (1998) Biochem. J. 330 611-614). These fatty acids are not present in S. cerevisiae but serve as the specific substrates for either the Δ⁶ or Δ⁵-desaturase, respectively. Expression of the L4 coding region from the GAL1 promoter of the vector was induced by the addition of galactose to 1%. Growth of the cultures was continued for 16 hours before removal of aliquots for the analysis of fatty acids by GC Total fatty acids extracted from yeast cultures were analysed by gas chromatography (GC) of methyl esters. Lipids were transmethylated with 1M HCl in methanol at 80° C. for 1 hr, then fatty acid methyl esters (FAMEs) were extracted in hexane. GC analysis of FAMEs were conducted using a Hewlett Packard 5880A Series Gas chromatograph equipped with a 25 M×0.32 mm RSL-500 BP bonded capillary column and a flame ionization detector. Fatty acids were identified by comparison with retention times of FAME standards (Sigma). Relative percentages of the fatty acids were estimated from peak areas. Arachidonic acid was identified by GC-MS using a Krats MS80RFA operating at an ionization voltage of 70 eV, with a scan range of 500-40 daltons. FIG. 4 shows the result of GC analysis of the fatty acid methyl esters of transformed yeast strains. An additional peak is apparent in the trace obtained from induced pYES2/L4 grown in the presence of di-homo-γ-linolenic acid compared to an empty-vector control. This peak was also absent from uninduced cultures grown on di-homo-γ-linolenic acid and it is also important to note that pYES2/L4 grown in the presence of linoleic acid failed to accumulate any novel peaks indicating that this fatty acid is not a substrate for the enzyme encoded by the C. elgans cDNA. The retention time of the additional peak is identical to that of the authentic methyl-arachidonic acid standard. The fatty acid produced from di-homo-γ-linolenic acid was further characterised by GCMS (Gas Chromatography Mass Spectrometry) and identified as arachidonic acid. The results show, therefore, that yeast cells transformed with the plasmid pYES2/L4 had acquired functional Δ⁵-desaturase activity and were now capable of synthesising arachidonic acid from the substrate di-homo-γ-linolenic acid. The Δ⁵-desaturase in the transformed yeast appeared to be an efficient catalyst.

[0108] This demonstrates that the DNA sequence from C. elegans encodes a functional polypeptide involved in the synthesis of arachidonic acid in the presence of galactose and di-homo-γ-linolenate.    1 ATGGTATTAC GAGAGCAAGA GCATGAGCCA TTCTTCATTA AAATTGATGG SEQ. 2   51 AAAATGGTGT CAAATTGACG ATGCTGTCCT GAGATCACAT CCAGGTGGTA  101 GTGCAATTAC TACCTATAAA AATATGGATG CCACTACCGT ATTCCACACA  151 TTCCATACTG GTTCTAAAGA AGCGTATCAA TGGCTGACAG AATTGAAAAA  201 AGAGTGCCCT ACACAAGAAC CAGAGATCCC AGATATTAAG GATGACCCAA  251 TCAAAGGAAT TGATGATGTG AACATGGGAA CTTTCAATAT TTCTGAGAAA  301 CGATCTGCCC AAATAAATAA AAGTTTCACT GATCTACGTA TGCGAGTTCG  351 TGCAGAAGGA CTTATGGATG GATCTCCTTT GTTCTACATT AGAAAAATTC  401 TTGAAACAAT CTTCACAATT CTTTTTGCAT TCTACCTTCA ATACCACACA  451 TATTATCTTC CATCAGCTAT TCTAATGGGA GTTGCGTGGC AACAATTGGG  501 ATGGTTAATC CATGAATTCG CACATCATCA GTTGTTCAAA AACAGATACT  551 ACAATGATTT GGCCAGCTAT TTCGTTGGAA ACTTTTTACA AGGATTCTCA  601 TCTGGTGGTT GGAAAGAGCA GCACAATGTG CATCACGCAG CCACAAATGT  651 TGTTGGACGA GACGGAGATC TTGATTTAGT CCCATTCTAT GCTACAGTGG  701 CAGAACATCT CAACAATTAT TCTCAGGATT CATGGGTTAT GACTCTATTC  751 AGATGGCAAC ATGTTCATTG GACATTCATG TTACCATTCC TCCGTCTCTC  801 GTGGCTTCTT CAGTCAATCA TTTTTGTTAG TCAGATGCCA ACTCATTATT  851 ATGACTATTA CAGAAATACT GCGATTTATG AACAGGTTGG TCTCTCTTTG  901 CACTGGGCTT GGTCATTGGG TCAATTGTAT TTCCTACCCG ATTGGTCAAC  951 TAGAATAATG TTCTTCCTTG TTTCTCATCT TGTTGGAGGT TTCCTGCTCT 1001 CTCATGTAGT TACTTTCAAT CATTATTCAG TGGAGAAGTT TGCATTGAGC 1051 TCGAACATCA TGTCAAATTA CGCTTGTCTT CAAATCATGA CCACAAGAAA 1101 TATGAGACCT GGAAGATTCA TTGACTGGCT TTGGGGAGGT CTTAACTATC 1151 AGATTGAGCA CCATCTTTTC CCAACGATGC CACGACACAA CTTGAACACT 1201 GTTATGCCAC TTGTTAAGGA GTTTGCAGCA GCAAATGGTT TACCATACAT 1251 GGTCGACGAT TATTTCACAG GATTCTGGCT TGAAATTGAG CAATTCCGAA 1301 ATATTGCAAA TGTTGCTGCT AAATTGACTA AAAAGATTGC CTAG    1 MGTDQGKTFT WEELAAHNTK GDLFLAIRGR VYDVTKFLSR HPGGVDTLLL SEQ. 3   51 GAGRDVTPVF EMYHAFGAAD AIMKKYYVGT LVSNELPVFP EPTVFHKTIK  101 TRVEGYFTDR DIDPKNRPEI WGRYALIFGS LIASYYAQLF VPFVVERTWL  151 QVVFAIIMGF ACAQVGLNPL HDASHFSVTH NPTVWKILGA THDFFNGASY  201 LVWMYQHMLG HHPYTNIAGA DPDVSTFEPD VRRIKPNQKW FVNHINQDMF  251 VPFLYGLLAF KVRIQDINIL YFVKTNDAIR VNPISTWHTV MFWGGKAFFV  301 WYRLIVPLQY LPLGKVLLLF TVADMVSSYW LALTFQANHV VEEVQWPLPD  351 ENGIIQKDWA AMQVETTQDY AHDSHLWTSI TGSLNYQAVH HLFPNVSQHH  401 YPDILAIIKN TCSEYKVPYL VKDTFWQAFA SHLEHLRVLG LRPKEE* The predicted amino acid sequence of L4 the gene which encodes a Δ⁵ fatty acid desaturase from C. elegans.    1 MVLREQEHEP FFIKIDGKWC QIDDAVLRSH PGGSAITTYK NMDATTVFHT SEQ 4   51 FHTGSKEAYQ WLTELKKECP TQEPEIPDIK DDPIKGIDDV NMGTFNISEK  101 RSAQINKSFT DLRMRVRAEG LMDGSPLFYI RKILETIFTI LFAFYLQYHT  151 YYLPSAILMG VAWQQLGWLI HEFAHHQLFK NRYYNDLASY FVGNFLQGFS  201 SGGWKEQHNV HHAATNVVGR DGDLDLVPFY ATVAEHLNNY SQDSWVMTLF  251 RWQHVHWTFM LPFLRLSWLL QSIIFVSQMP THYYDYYRNT AIYEQVGLSL  301 HWAWSLGQLY FLPDWSTRIM FFLVSHLVGG FLLSHVVTFN HYSVEKFALS  351 SNIMSNYACL QIMTTRNMRP GRFIDWLWGG LNYQIEHHLP PTMPRHNLNT  401 VMPLVKEFAA ANGLPYMVDD YFTGFWLEIE QFRNIANVAA KLTKKIA*

[0109]

1 23 1 1405 DNA Mortierella alpina 1 atgggtacgg accaaggaaa aaccttcacc tgggaagagc tagcggccca taacaccaag 60 ggcgaccttt ttttggccat ccgcggcagg gtgtacgatg tcacaaagtt cttgagccgc 120 catcctggtg gagtggacac tctcctgctc ggagctggcc gagatgttac tccggtcttt 180 gagatgtatc acgcgtttgg ggctgcagat gccatcatga agaagtacta tgtcggtaca 240 ttggtttcga atgagctgcc cgtcttcccg gagccaacgg tgttccacaa aaccatcaag 300 acgagagttg agggctactt tacggatcgg gacattgatc ccaagaacag accagagatc 360 tggggacgat acgctcttat ctttggatcc ttgatcgctt cctactacgc gcagctcttt 420 gtgcctttcg ttgtcgaacg cacatggctc caggtggtgt ttgcaatcat catgggattt 480 gcgtgcgcac aagtcggact caaccctctt catgatgcgt ctcacttttc agtgacccac 540 aaccccactg tctggaagat tctgggagcc acgcacgact ttttcaacgg agcatcgtac 600 ctggtgtgga tgtaccaaca tatgctcggc catcacccct acaccaacat tgctggagca 660 gatcctgacg tgtcgacgtt tgagcccgat gttcgtcgta tcaagcccaa ccaaaagtgg 720 tttgttaacc acatcaacca ggacatgttt gttcctttcc tgtacggact gctggcgttc 780 aaggtgcgca ttcaggacat caacattttg tactttgtca agacaaatga cgcaattcgc 840 gtcaatccca tctcgacatg gcacactgtg atgttctggg gcggcaaggc tttctttgtc 900 tggtatcgcc tgattgttcc cctgcagtat ctgcccctgg gcaaggtgct gctcctgttc 960 acggtcgcgg acatggtgtc gtcttactgg ctggcgctga ccttccaggc gaaccacgtt 1020 gttgaggaag ttcagtggcc gttgcctgac gagaacggga tcatccaaaa ggactgggca 1080 gctatgcagg ttgagactac gcaggattac gcacacgact cgcacctctg gaccagcatt 1140 actggcagct tgaactacca ggctgtgcac catctgttcc ccaacgtgtc gcagcaccat 1200 tatcccgata ttctggccat catcaagaac acctgcagcg agtacaaggt tccatacctt 1260 gtcaaggata ccttttggca agcatttgct tcacatttgg agcacttgcg tgttcttgga 1320 ctccgtccca aggaagagta gaaagaaaaa aagcgccgaa cgaagtattg cccccttttt 1380 ctccaagaaa aaaaaaaaaa aaaaa 1405 2 1344 DNA C. elegans 2 atggtattac gagagcaaga gcatgagcca ttcttcatta aaattgatgg aaaatggtgt 60 caaattgacg atgctgtcct gagatcacat ccaggtggta gtgcaattac tacctataaa 120 aatatggatg ccactaccgt attccacaca ttccatactg gttctaaaga agcgtatcaa 180 tggctgacag aattgaaaaa agagtgccct acacaagaac cagagatccc agatattaag 240 gatgacccaa tcaaaggaat tgatgatgtg aacatgggaa ctttcaatat ttctgagaaa 300 cgatctgccc aaataaataa aagtttcact gatctacgta tgcgagttcg tgcagaagga 360 cttatggatg gatctccttt gttctacatt agaaaaattc ttgaaacaat cttcacaatt 420 ctttttgcat tctaccttca ataccacaca tattatcttc catcagctat tctaatggga 480 gttgcgtggc aacaattggg atggttaatc catgaattcg cacatcatca gttgttcaaa 540 aacagatact acaatgattt ggccagctat ttcgttggaa actttttaca aggattctca 600 tctggtggtt ggaaagagca gcacaatgtg catcacgcag ccacaaatgt tgttggacga 660 gacggagatc ttgatttagt cccattctat gctacagtgg cagaacatct caacaattat 720 tctcaggatt catgggttat gactctattc agatggcaac atgttcattg gacattcatg 780 ttaccattcc tccgtctctc gtggcttctt cagtcaatca tttttgttag tcagatgcca 840 actcattatt atgactatta cagaaatact gcgatttatg aacaggttgg tctctctttg 900 cactgggctt ggtcattggg tcaattgtat ttcctacccg attggtcaac tagaataatg 960 ttcttccttg tttctcatct tgttggaggt ttcctgctct ctcatgtagt tactttcaat 1020 cattattcag tggagaagtt tgcattgagc tcgaacatca tgtcaaatta cgcttgtctt 1080 caaatcatga ccacaagaaa tatgagacct ggaagattca ttgactggct ttggggaggt 1140 cttaactatc agattgagca ccatcttttc ccaacgatgc cacgacacaa cttgaacact 1200 gttatgccac ttgttaagga gtttgcagca gcaaatggtt taccatacat ggtcgacgat 1260 tatttcacag gattctggct tgaaattgag caattccgaa atattgcaaa tgttgctgct 1320 aaattgacta aaaagattgc ctag 1344 3 446 PRT Mortierella alpina 3 Met Gly Thr Asp Gln Gly Lys Thr Phe Thr Trp Glu Glu Leu Ala Ala 1 5 10 15 His Asn Thr Lys Gly Asp Leu Phe Leu Ala Ile Arg Gly Arg Val Tyr 20 25 30 Asp Val Thr Lys Phe Leu Ser Arg His Pro Gly Gly Val Asp Thr Leu 35 40 45 Leu Leu Gly Ala Gly Arg Asp Val Thr Pro Val Phe Glu Met Tyr His 50 55 60 Ala Phe Gly Ala Ala Asp Ala Ile Met Lys Lys Tyr Tyr Val Gly Thr 65 70 75 80 Leu Val Ser Asn Glu Leu Pro Val Phe Pro Glu Pro Thr Val Phe His 85 90 95 Lys Thr Ile Lys Thr Arg Val Glu Gly Tyr Phe Thr Asp Arg Asp Ile 100 105 110 Asp Pro Lys Asn Arg Pro Glu Ile Trp Gly Arg Tyr Ala Leu Ile Phe 115 120 125 Gly Ser Leu Ile Ala Ser Tyr Tyr Ala Gln Leu Phe Val Pro Phe Val 130 135 140 Val Glu Arg Thr Trp Leu Gln Val Val Phe Ala Ile Ile Met Gly Phe 145 150 155 160 Ala Cys Ala Gln Val Gly Leu Asn Pro Leu His Asp Ala Ser His Phe 165 170 175 Ser Val Thr His Asn Pro Thr Val Trp Lys Ile Leu Gly Ala Thr His 180 185 190 Asp Phe Phe Asn Gly Ala Ser Tyr Leu Val Trp Met Tyr Gln His Met 195 200 205 Leu Gly His His Pro Tyr Thr Asn Ile Ala Gly Ala Asp Pro Asp Val 210 215 220 Ser Thr Phe Glu Pro Asp Val Arg Arg Ile Lys Pro Asn Gln Lys Trp 225 230 235 240 Phe Val Asn His Ile Asn Gln Asp Met Phe Val Pro Phe Leu Tyr Gly 245 250 255 Leu Leu Ala Phe Lys Val Arg Ile Gln Asp Ile Asn Ile Leu Tyr Phe 260 265 270 Val Lys Thr Asn Asp Ala Ile Arg Val Asn Pro Ile Ser Thr Trp His 275 280 285 Thr Val Met Phe Trp Gly Gly Lys Ala Phe Phe Val Trp Tyr Arg Leu 290 295 300 Ile Val Pro Leu Gln Tyr Leu Pro Leu Gly Lys Val Leu Leu Leu Phe 305 310 315 320 Thr Val Ala Asp Met Val Ser Ser Tyr Trp Leu Ala Leu Thr Phe Gln 325 330 335 Ala Asn His Val Val Glu Glu Val Gln Trp Pro Leu Pro Asp Glu Asn 340 345 350 Gly Ile Ile Gln Lys Asp Trp Ala Ala Met Gln Val Glu Thr Thr Gln 355 360 365 Asp Tyr Ala His Asp Ser His Leu Trp Thr Ser Ile Thr Gly Ser Leu 370 375 380 Asn Tyr Gln Ala Val His His Leu Phe Pro Asn Val Ser Gln His His 385 390 395 400 Tyr Pro Asp Ile Leu Ala Ile Ile Lys Asn Thr Cys Ser Glu Tyr Lys 405 410 415 Val Pro Tyr Leu Val Lys Asp Thr Phe Trp Gln Ala Phe Ala Ser His 420 425 430 Leu Glu His Leu Arg Val Leu Gly Leu Arg Pro Lys Glu Glu 435 440 445 4 448 PRT C. elegans 4 Met Val Leu Arg Glu Gln Glu His Glu Pro Phe Phe Ile Lys Ile Asp 1 5 10 15 Gly Lys Trp Cys Gln Ile Asp Asp Ala Val Leu Arg Ser His Pro Gly 20 25 30 Gly Ser Ala Ile Thr Thr Tyr Lys Asn Met Asp Ala Thr Thr Val Phe 35 40 45 His Thr Phe His Thr Gly Ser Lys Glu Ala Tyr Gln Trp Leu Thr Glu 50 55 60 Lys Leu Lys Lys Glu Cys Pro Thr Gln Glu Pro Glu Ile Pro Asp Ile 65 70 75 80 Lys Asp Asp Pro Ile Lys Gly Ile Asp Asp Val Asn Met Gly Thr Phe 85 90 95 Asn Ile Ser Glu Lys Arg Ser Ala Gln Ile Asn Lys Ser Phe Thr Asp 100 105 110 Leu Arg Met Arg Val Arg Ala Glu Gly Leu Met Gly Asp Ser Pro Leu 115 120 125 Phe Tyr Ile Arg Lys Ile Leu Glu Thr Ile Phe Thr Ile Leu Phe Ala 130 135 140 Phe Tyr Leu Gln Tyr His Thr Tyr Tyr Leu Pro Ser Ala Ile Leu Met 145 150 155 160 Gly Val Ala Trp Gln Gln Leu Gly Trp Leu Ile His Glu Phe Ala His 165 170 175 His Gln Leu Phe Lys Asn Arg Tyr Tyr Asn Asp Leu Ala Ser Tyr Phe 180 185 190 Val Gly Asn Phe Leu Gln Gly Phe Ser Ser Gly Gly Trp Lys Glu Gln 195 200 205 His Asn Val His His Ala Ala Thr Asn Val Val Gly Arg Asp Gly Asp 210 215 220 Leu Asp Leu Val Pro Phe Tyr Ala Thr Val Ala Glu His Leu Asn Asn 225 230 235 240 Tyr Ser Gln Asp Ser Trp Val Met Thr Leu Phe Arg Trp Gln His Val 245 250 255 His Trp Thr Phe Met Leu Pro Phe Leu Arg Leu Ser Trp Leu Leu Gln 260 265 270 Ser Ile Ile Phe Val Ser Gln Met Pro Thr His Tyr Tyr Asp Tyr Tyr 275 280 285 Arg Asn Thr Ala Ile Tyr Glu Gln Val Gly Leu Ser Leu His Trp Ala 290 295 300 Trp Ser Leu Gly Gln Leu Tyr Phe Leu Pro Asp Trp Ser Thr Arg Ile 305 310 315 320 Met Phe Phe Leu Val Ser His Leu Val Gly Gly Phe Leu Leu Ser His 325 330 335 Val Val Thr Phe Asn His Tyr Ser Val Glu Lys Phe Ala Leu Ser Ser 340 345 350 Asn Ile Met Ser Asn Tyr Ala Cys Leu Gln Ile Met Thr Thr Arg Asn 355 360 365 Met Arg Pro Gly Arg Phe Ile Asp Trp Leu Trp Gly Gly Leu Asn Tyr 370 375 380 Gln Ile Glu His His Leu Phe Pro Thr Met Pro Arg His Asn Leu Asn 385 390 395 400 Thr Val Met Pro Leu Tyr Lys Glu Phe Ala Ala Ala Asn Gly Leu Pro 405 410 415 Tyr Met Val Asp Asp Tyr Phe Thr Gly Phe Trp Leu Glu Ile Glu Gln 420 425 430 Phe Arg Asn Ile Ala Asn Val Ala Ala Lys Leu Thr Lys Lys Ile Ala 435 440 445 5 24 DNA Artificial Sequence PCR primer 5 gcgaattawt ggcaygaytg ygca 24 6 25 DNA Artificial Sequence PCR primer 6 gcgaattcat tkggraaarr tgrtg 25 7 18 DNA Artificial Sequence PCR primer 7 gatgcgtctc acttttca 18 8 21 DNA Artificial Sequence PCR primer 8 gtggtgcaca gcctggtagt t 21 9 351 PRT Spirulina 9 Met Thr Leu Ser Ile Val Lys Ser Glu Asp Ser Ser Ser Arg Pro Ser 1 5 10 15 Ala Val Pro Ser Asp Leu Pro Leu Glu Glu Asp Ile Ile Asn Thr Leu 20 25 30 Pro Ser Gly Val Phe Val Gln Asp Arg Tyr Lys Ala Trp Met Thr Val 35 40 45 Ile Ile Asn Val Val Met Val Gly Leu Gly Trp Leu Gly Ile Ala Ile 50 55 60 Ala Pro Trp Phe Leu Leu Pro Val Val Trp Val Phe Thr Gly Thr Ala 65 70 75 80 Leu Thr Gly Phe Phe Val Ile Gly His Asp Cys Gly His Arg Ser Phe 85 90 95 Ser Arg Asn Val Trp Val Asn Asp Trp Val Gly His Ile Leu Phe Leu 100 105 110 Pro Ile Ile Tyr Pro Phe His Ser Trp Arg Ile Gly His Asn Gln His 115 120 125 His Lys Tyr Thr Asn Arg Met Glu Leu Asp Asn Ala Trp Gln Pro Trp 130 135 140 Arg Lys Glu Glu Tyr Gln Asn Ala Gly Lys Phe Met Gln Val Thr Tyr 145 150 155 160 Asp Leu Phe Arg Gly Arg Ala Trp Trp Ile Gly Ser Ile Leu His Trp 165 170 175 Ala Ser Ile His Phe Asp Trp Thr Lys Phe Glu Gly Lys Gln Arg Gln 180 185 190 Gln Val Lys Phe Ser Ser Leu Leu Val Ile Gly Ala Ala Ala Ile Ala 195 200 205 Phe Pro Thr Met Ile Leu Thr Ile Gly Val Trp Gly Phe Val Lys Phe 210 215 220 Trp Val Ile Pro Trp Leu Val Phe His Phe Trp Met Ser Thr Phe Thr 225 230 235 240 Leu Leu His His Thr Ile Ala Asp Ile Pro Phe Arg Glu Pro Glu Gln 245 250 255 Trp His Glu Ala Glu Ser Gln Leu Ser Gly Thr Val His Cys Asn Tyr 260 265 270 Ser Arg Trp Gly Glu Phe Leu Cys His Asp Ile Asn Val His Ile Pro 275 280 285 His His Val Thr Thr Ala Ile Pro Trp Tyr Asn Leu Arg Thr Pro Thr 290 295 300 Pro Val Tyr Arg Lys Ile Gly Gly Glu Tyr Leu Tyr Pro Glu Cys Asp 305 310 315 320 Phe Ser Trp Gly Leu Met Lys Gln Val Val Asp His Ala Ile Cys Met 325 330 335 Met Arg Ile Thr Ile Ile Ser Gln Ser Leu Thr Thr Lys Arg Val 340 345 350 10 368 PRT Spirulina 10 Met Thr Ser Thr Thr Ser Lys Val Thr Phe Gly Lys Ser Ile Gly Phe 1 5 10 15 Arg Lys Glu Leu Asn Arg Arg Val Asn Ala Tyr Leu Glu Ala Glu Asn 20 25 30 Ile Ser Pro Arg Asp Asn Pro Pro Met Tyr Leu Lys Thr Ala Ile Ile 35 40 45 Leu Ala Trp Val Val Ser Ala Trp Thr Phe Val Val Phe Gly Pro Asp 50 55 60 Val Leu Trp Met Lys Leu Leu Gly Cys Ile Val Leu Gly Phe Gly Val 65 70 75 80 Ser Ala Val Gly Phe Asn Ile Ser His Asp Gly Asn His Gly Gly Tyr 85 90 95 Ser Lys Tyr Gln Trp Val Asn Tyr Leu Ser Gly Leu Thr His Asp Ala 100 105 110 Ile Gly Val Ser Ser Tyr Leu Trp Lys Phe Arg His Asn Val Leu His 115 120 125 His Thr Tyr Thr Asn Ile Leu Gly His Asp Val Glu Ile His Gly Asp 130 135 140 Glu Leu Val Arg Met Ser Pro Ser Met Glu Tyr Arg Trp Tyr His Arg 145 150 155 160 Tyr Gln His Trp Phe Ile Trp Phe Val Tyr Pro Phe Ile Pro Tyr Tyr 165 170 175 Trp Ser Ile Ala Asp Val Gln Thr Met Leu Phe Lys Arg Gln Tyr His 180 185 190 Asp His Glu Ile Pro Ser Pro Thr Trp Val Asp Ile Ala Thr Leu Leu 195 200 205 Ala Phe Lys Ala Phe Gly Val Ala Val Phe Leu Ile Ile Pro Ile Ala 210 215 220 Val Gly Tyr Ser Pro Leu Glu Ala Val Ile Gly Ala Ser Ile Val Tyr 225 230 235 240 Met Thr His Gly Leu Val Ala Cys Val Val Phe Met Leu Ala His Val 245 250 255 Ile Glu Pro Ala Glu Phe Leu Asp Pro Asp Asn Leu His Ile Asp Asp 260 265 270 Glu Trp Ala Ile Ala Gln Val Lys Thr Thr Val Asp Phe Ala Pro Asn 275 280 285 Asn Pro Ile Ile Asn Trp Tyr Val Gly Gly Leu Asn Tyr Gln Thr Val 290 295 300 His His Leu Phe Pro His Ile Cys His Ile His Tyr Pro Lys Ile Ala 305 310 315 320 Pro Ile Leu Ala Glu Val Cys Glu Glu Phe Gly Val Asn Tyr Ala Val 325 330 335 His Gln Thr Phe Phe Gly Ala Leu Ala Ala Asn Tyr Ser Trp Leu Lys 340 345 350 Lys Met Ser Ile Asn Pro Glu Thr Lys Ala Ile Glu Gln Leu Thr Val 355 360 365 11 458 PRT Helianthus annus 11 Met Val Ser Pro Ser Ile Glu Val Leu Asn Ser Ile Ala Asp Gly Lys 1 5 10 15 Lys Tyr Ile Thr Ser Lys Glu Leu Lys Lys His Asn Asn Pro Asn Asp 20 25 30 Leu Trp Ile Ser Ile Leu Gly Lys Val Tyr Asn Val Thr Glu Trp Ala 35 40 45 Lys Glu His Pro Gly Gly Asp Ala Pro Leu Ile Asn Leu Ala Gly Gln 50 55 60 Asp Val Thr Asp Ala Phe Ile Ala Phe His Pro Gly Thr Ala Trp Lys 65 70 75 80 His Leu Asp Lys Leu Phe Thr Gly Tyr His Leu Lys Asp Tyr Gln Val 85 90 95 Ser Asp Ile Ser Arg Asp Tyr Arg Lys Leu Ala Ser Glu Phe Ala Lys 100 105 110 Ala Gly Met Phe Glu Lys Lys Gly His Gly Val Ile Tyr Ser Leu Cys 115 120 125 Phe Val Ser Leu Leu Leu Ser Ala Cys Val Tyr Gly Val Leu Tyr Ser 130 135 140 Gly Ser Phe Trp Ile His Met Leu Ser Gly Ala Ile Leu Gly Leu Ala 145 150 155 160 Trp Met Gln Ile Ala Tyr Leu Gly His Asp Ala Gly His Tyr Gln Met 165 170 175 Met Ala Thr Arg Gly Trp Asn Lys Phe Ala Gly Ile Phe Ile Gly Asn 180 185 190 Cys Ile Thr Gly Ile Ser Ile Ala Trp Trp Lys Trp Thr His Asn Ala 195 200 205 His His Ile Ala Cys Asn Ser Leu Asp Tyr Asp Pro Asp Leu Gln His 210 215 220 Leu Pro Met Leu Ala Val Ser Ser Lys Leu Phe Asn Ser Ile Thr Ser 225 230 235 240 Val Phe Tyr Gly Arg Gln Leu Thr Phe Asp Pro Leu Ala Arg Phe Phe 245 250 255 Val Ser Tyr Gln His Tyr Leu Tyr Tyr Pro Ile Met Cys Val Ala Arg 260 265 270 Val Asn Leu Tyr Leu Gln Thr Ile Leu Leu Leu Ile Ser Lys Arg Lys 275 280 285 Ile Pro Asp Arg Gly Leu Asn Ile Leu Gly Thr Leu Ile Phe Trp Thr 290 295 300 Trp Phe Pro Leu Leu Val Ser Arg Leu Pro Asn Trp Pro Glu Arg Val 305 310 315 320 Ala Phe Val Leu Val Ser Phe Cys Val Thr Gly Ile Gln His Ile Gln 325 330 335 Phe Thr Leu Asn His Phe Ser Gly Asp Val Tyr Val Gly Pro Pro Lys 340 345 350 Gly Asp Asn Trp Phe Glu Lys Gln Thr Arg Gly Thr Ile Asp Ile Ala 355 360 365 Cys Ser Ser Trp Met Asp Trp Phe Phe Gly Gly Leu Gln Phe Gln Leu 370 375 380 Glu His His Leu Phe Pro Arg Leu Pro Arg Cys His Leu Arg Ser Ile 385 390 395 400 Ser Pro Ile Cys Arg Glu Leu Cys Lys Lys Tyr Asn Leu Pro Tyr Val 405 410 415 Ser Leu Ser Phe Tyr Asp Ala Asn Val Thr Thr Leu Lys Thr Leu Arg 420 425 430 Thr Ala Ala Leu Gln Ala Arg Asp Leu Thr Asn Pro Ala Pro Gln Asn 435 440 445 Leu Ala Trp Glu Ala Phe Asn Thr His Gly 450 455 12 359 PRT Synechocystis sp. 12 Met Leu Thr Ala Glu Arg Ile Lys Phe Thr Gln Lys Arg Gly Phe Arg 1 5 10 15 Arg Val Leu Asn Gln Arg Val Asp Ala Tyr Phe Ala Glu His Gly Leu 20 25 30 Thr Gln Arg Asp Asn Pro Ser Met Tyr Leu Lys Thr Leu Ile Ile Val 35 40 45 Leu Trp Leu Phe Ser Ala Trp Ala Phe Val Leu Phe Ala Pro Val Ile 50 55 60 Phe Pro Val Arg Leu Leu Gly Cys Met Val Leu Ala Ile Ala Leu Ala 65 70 75 80 Ala Phe Ser Phe Asn Val Gly His Asp Ala Asn His Asn Ala Tyr Ser 85 90 95 Ser Asn Pro His Ile Asn Arg Val Leu Gly Met Thr Tyr Asp Phe Val 100 105 110 Gly Leu Ser Ser Phe Leu Trp Arg Tyr Arg His Asn Tyr Leu His His 115 120 125 Thr Tyr Thr Asn Ile Leu Gly His Asp Val Glu Ile His Gly Asp Gly 130 135 140 Ala Val Arg Met Ser Pro Glu Gln Glu His Val Gly Ile Tyr Arg Phe 145 150 155 160 Gln Gln Phe Tyr Ile Trp Gly Leu Tyr Leu Phe Ile Pro Phe Tyr Trp 165 170 175 Phe Leu Tyr Asp Val Tyr Leu Val Leu Asn Lys Gly Lys Tyr His Asp 180 185 190 His Lys Ile Pro Pro Phe Gln Pro Leu Glu Leu Ala Ser Leu Leu Gly 195 200 205 Ile Lys Leu Leu Trp Leu Gly Tyr Val Phe Gly Leu Pro Leu Ala Leu 210 215 220 Gly Phe Ser Ile Pro Glu Val Leu Ile Gly Ala Ser Val Thr Tyr Met 225 230 235 240 Thr Tyr Gly Ile Val Val Cys Thr Ile Phe Met Leu Ala His Val Leu 245 250 255 Glu Ser Thr Glu Phe Leu Thr Pro Asp Gly Glu Ser Gly Ala Ile Asp 260 265 270 Asp Glu Trp Ala Ile Cys Gln Ile Arg Thr Thr Ala Asn Phe Ala Thr 275 280 285 Asn Asn Pro Phe Trp Asn Trp Phe Cys Gly Gly Leu Asn His Gln Val 290 295 300 Thr His His Leu Phe Pro Asn Ile Cys His Ile His Tyr Pro Gln Leu 305 310 315 320 Glu Asn Ile Ile Lys Asp Val Cys Gln Glu Phe Gly Val Glu Tyr Lys 325 330 335 Val Tyr Pro Thr Phe Lys Ala Ala Ile Ala Ser Asn Tyr Arg Trp Leu 340 345 350 Glu Ala Met Gly Lys Ala Ser 355 13 448 PRT Borago officinalis 13 Met Ala Ala Gln Ile Lys Lys Tyr Ile Thr Ser Asp Glu Leu Lys Asn 1 5 10 15 His Asp Lys Pro Gly Asp Leu Trp Ile Ser Ile Gln Gly Lys Ala Tyr 20 25 30 Asp Val Ser Asp Trp Val Lys Asp His Pro Gly Gly Ser Phe Pro Leu 35 40 45 Lys Ser Leu Ala Gly Gln Glu Val Thr Asp Ala Phe Val Ala Phe His 50 55 60 Pro Ala Ser Thr Trp Lys Asn Leu Asp Lys Phe Phe Thr Gly Tyr Tyr 65 70 75 80 Leu Lys Asp Tyr Ser Val Ser Glu Val Ser Lys Asp Tyr Arg Lys Leu 85 90 95 Val Phe Glu Phe Ser Lys Met Gly Leu Tyr Asp Lys Lys Gly His Ile 100 105 110 Met Phe Ala Thr Leu Cys Phe Ile Ala Met Leu Phe Ala Met Ser Val 115 120 125 Tyr Gly Val Leu Phe Cys Glu Gly Val Leu Val His Leu Phe Ser Gly 130 135 140 Cys Leu Met Gly Phe Leu Trp Ile Gln Ser Gly Trp Ile Gly His Asp 145 150 155 160 Ala Gly His Tyr Met Val Val Ser Asp Ser Arg Leu Asn Lys Phe Met 165 170 175 Gly Ile Phe Ala Ala Asn Cys Leu Ser Gly Ile Ser Ile Gly Trp Trp 180 185 190 Lys Trp Asn His Asn Ala His His Ile Ala Cys Asn Ser Leu Glu Tyr 195 200 205 Asp Pro Asp Leu Gln Tyr Ile Pro Phe Leu Val Val Ser Ser Lys Phe 210 215 220 Phe Gly Ser Leu Thr Ser His Phe Tyr Glu Lys Arg Leu Thr Phe Asp 225 230 235 240 Ser Leu Ser Arg Phe Phe Val Ser Tyr Gln His Trp Thr Phe Tyr Pro 245 250 255 Ile Met Cys Ala Ala Arg Leu Asn Met Tyr Val Gln Ser Leu Ile Met 260 265 270 Leu Leu Thr Lys Arg Asn Val Ser Tyr Arg Ala His Glu Leu Leu Gly 275 280 285 Cys Leu Val Phe Ser Ile Trp Tyr Pro Leu Leu Val Ser Cys Leu Pro 290 295 300 Asn Trp Gly Glu Arg Ile Met Phe Val Ile Ala Ser Leu Ser Val Thr 305 310 315 320 Gly Met Gln Gln Val Gln Phe Ser Leu Asn His Phe Ser Ser Ser Val 325 330 335 Tyr Val Gly Lys Pro Lys Gly Asn Asn Trp Phe Glu Lys Gln Thr Asp 340 345 350 Gly Thr Leu Asp Ile Ser Cys Pro Pro Trp Met Asp Trp Phe His Gly 355 360 365 Gly Leu Gln Phe Gln Ile Glu His His Leu Phe Pro Lys Met Pro Arg 370 375 380 Cys Asn Leu Arg Lys Ile Ser Pro Tyr Val Ile Glu Leu Cys Lys Lys 385 390 395 400 His Asn Leu Pro Tyr Asn Tyr Ala Ser Phe Ser Lys Ala Asn Glu Met 405 410 415 Thr Leu Arg Thr Leu Arg Asn Thr Ala Leu Gln Ala Arg Asp Ile Thr 420 425 430 Lys Pro Leu Pro Lys Asn Leu Val Trp Glu Ala Leu His Thr His Gly 435 440 445 14 446 PRT Morierella alpina 14 Met Gly Thr Asp Gln Gly Lys Thr Phe Thr Trp Glu Glu Leu Ala Ala 1 5 10 15 His Asn Thr Lys Gly Asp Leu Phe Leu Ala Ile Arg Gly Arg Val Tyr 20 25 30 Asp Val Thr Lys Phe Leu Ser Arg His Pro Gly Gly Val Asp Thr Leu 35 40 45 Leu Leu Gly Ala Gly Arg Asp Val Thr Pro Val Phe Glu Met Tyr His 50 55 60 Ala Phe Gly Ala Ala Asp Ala Ile Met Lys Lys Tyr Tyr Val Gly Thr 65 70 75 80 Leu Val Ser Asn Glu Leu Pro Val Phe Pro Glu Pro Thr Val Phe His 85 90 95 Lys Thr Ile Lys Thr Arg Val Glu Gly Tyr Phe Thr Asp Arg Asp Ile 100 105 110 Asp Pro Lys Asn Arg Pro Glu Ile Trp Gly Arg Tyr Ala Leu Ile Phe 115 120 125 Gly Ser Leu Ile Ala Ser Tyr Tyr Ala Gln Leu Phe Val Pro Phe Val 130 135 140 Val Glu Arg Thr Trp Leu Gln Val Val Phe Ala Ile Ile Met Gly Phe 145 150 155 160 Ala Cys Ala Gln Val Gly Leu Asn Pro Leu His Asp Ala Ser His Phe 165 170 175 Ser Val Thr His Asn Pro Thr Val Trp Lys Ile Leu Gly Ala Thr His 180 185 190 Asp Phe Phe Asn Gly Ala Ser Tyr Leu Val Trp Met Tyr Gln His Met 195 200 205 Leu Gly His His Pro Tyr Thr Asn Ile Ala Gly Ala Asp Pro Asp Val 210 215 220 Ser Thr Phe Glu Pro Asp Val Arg Arg Ile Lys Pro Asn Gln Lys Trp 225 230 235 240 Phe Val Asn His Ile Asn Gln Asp Met Phe Val Pro Phe Leu Tyr Gly 245 250 255 Leu Leu Ala Phe Lys Val Arg Ile Gln Asp Ile Asn Ile Leu Tyr Phe 260 265 270 Val Lys Thr Asn Asp Ala Ile Arg Val Asn Pro Ile Ser Thr Trp His 275 280 285 Thr Val Met Phe Trp Gly Gly Lys Ala Phe Phe Val Trp Tyr Arg Leu 290 295 300 Ile Val Pro Leu Gln Tyr Leu Pro Leu Gly Lys Val Leu Leu Leu Phe 305 310 315 320 Thr Val Ala Asp Met Val Ser Ser Tyr Trp Leu Ala Leu Thr Phe Gln 325 330 335 Ala Asn His Val Val Glu Glu Val Gln Trp Pro Leu Pro Asp Glu Asn 340 345 350 Gly Ile Ile Gln Lys Asp Trp Ala Ala Met Gln Val Glu Thr Thr Gln 355 360 365 Asp Tyr Ala His Asp Ser His Leu Trp Thr Ser Ile Thr Gly Ser Leu 370 375 380 Asn Tyr Gln Ala Val His His Leu Phe Pro Asn Val Ser Gln His His 385 390 395 400 Tyr Pro Asp Ile Leu Ala Ile Ile Lys Asn Thr Cys Ser Glu Tyr Lys 405 410 415 Val Pro Tyr Leu Val Lys Asp Thr Phe Trp Gln Ala Phe Ala Ser His 420 425 430 Leu Glu His Leu Arg Val Leu Gly Leu Arg Pro Lys Glu Glu 435 440 445 15 4 PRT Artificial Sequence cytochrome b5 domain motif 15 His Pro Gly Gly 1 16 20 DNA Artificial Sequence PCR primer 16 atggtattac gagagcaaga 20 17 20 DNA Artificial Sequence PCR primer 17 tctgggatct ctggttcttg 20 18 34 DNA Artificial Sequence PCR primer 18 gcgaagctta aaatggtatt acgagagcaa gagc 34 19 33 DNA Artificial Sequence PCR primer 19 gcgggatcca atctaggcaa tctttttagt caa 33 20 443 PRT C. elegans 20 Met Val Val Asp Lys Asn Ala Ser Gly Leu Arg Met Lys Val Asp Gly 1 5 10 15 Lys Trp Leu Tyr Leu Ser Glu Glu Leu Val Lys Lys His Pro Gly Gly 20 25 30 Ala Val Ile Glu Gln Tyr Lys Asn Ser Asp Ala Thr His Ile Phe His 35 40 45 Ala Phe His Glu Gly Ser Ser Gln Ala Tyr Lys Gln Leu Asp Leu Leu 50 55 60 Lys Lys His Gly Glu His Asp Glu Phe Leu Glu Lys Gln Leu Glu Lys 65 70 75 80 Arg Leu Asp Lys Val Asp Ile Asn Val Ser Ala Tyr Asp Val Ser Val 85 90 95 Ala Gln Glu Lys Lys Met Val Glu Ser Phe Glu Lys Leu Arg Gln Lys 100 105 110 Leu His Asp Asp Gly Leu Met Lys Ala Asn Glu Thr Tyr Phe Leu Phe 115 120 125 Lys Ala Ile Ser Thr Leu Ser Ile Met Ala Phe Ala Phe Tyr Leu Gln 130 135 140 Tyr Leu Gly Trp Tyr Ile Thr Ser Ala Cys Leu Leu Ala Leu Ala Trp 145 150 155 160 Gln Gln Phe Gly Trp Leu Thr His Glu Phe Cys His Gln Gln Pro Phe 165 170 175 Lys Asn Arg Pro Leu Asn Asp Thr Ile Ser Leu Phe Phe Gly Asn Phe 180 185 190 Leu Gln Gly Phe Ser Arg Asp Trp Trp Lys Asp Lys His Asn Thr His 195 200 205 His Ala Ala Thr Asn Val Ile Asp His Asp Gly Asp Ile Asp Leu Ala 210 215 220 Pro Leu Phe Ala Phe Ile Pro Gly Asp Leu Cys Lys Tyr Lys Ala Ser 225 230 235 240 Phe Glu Lys Ala Ile Leu Lys Ile Val Pro Tyr Gln His Leu Tyr Phe 245 250 255 Thr Ala Met Leu Pro Met Leu Arg Phe Ser Trp Thr Gly Gln Ser Val 260 265 270 Gln Trp Val Phe Lys Glu Asn Gln Met Glu Tyr Lys Val Tyr Gln Arg 275 280 285 Asn Ala Phe Trp Glu Gln Ala Thr Ile Val Gly His Trp Ala Trp Val 290 295 300 Phe Tyr Gln Leu Phe Leu Leu Pro Thr Trp Pro Leu Arg Val Ala Tyr 305 310 315 320 Phe Ile Ile Ser Gln Met Gly Gly Gly Leu Leu Ile Ala His Val Val 325 330 335 Thr Phe Asn His Asn Ser Val Asp Lys Tyr Pro Ala Asn Ser Arg Ile 340 345 350 Leu Asn Asn Phe Ala Ala Leu Gln Ile Leu Thr Thr Arg Asn Met Thr 355 360 365 Pro Ser Pro Phe Ile Asp Trp Leu Trp Gly Gly Leu Asn Tyr Gln Ile 370 375 380 Glu His His Leu Phe Pro Thr Met Pro Arg Cys Asn Leu Asn Ala Cys 385 390 395 400 Val Lys Tyr Val Lys Glu Trp Cys Lys Glu Asn Asn Leu Pro Tyr Leu 405 410 415 Val Asp Asp Tyr Phe Asp Gly Tyr Ala Met Asn Leu Gln Gln Leu Lys 420 425 430 Asn Met Ala Glu His Ile Gln Ala Lys Ala Ala 435 440 21 5 PRT Artificial Sequence misc_feature (1)...(5) Xaa = any amino acid 21 Gln Xaa Xaa His His 1 5 22 5 PRT Artificial Sequence cytochrome b5-like heme-binding domain motif 22 Glu His Pro Gly Gly 1 5 23 5 PRT Artificial Sequence misc_feature (1)...(5) Xaa = any amino acid 23 His Xaa Xaa His His 1 5 

1. An isolated animal Δ5-fatty acid desaturase and functional portions thereof.
 2. Isolated C. elegans Δ5-fatty acid desaturase.
 3. A DNA sequence encoding a Δ5-fatty acid desaturase according to claim 1 or claim
 2. 4. A DNA sequence according to claim 3 and comprising at least a portion of the sequence shown in SEQ.2 and equivalents to that sequence, or to portions of that sequence, which encode a functional Δ5-fatty acid desaturase by virtue of the degeneracy of the genetic code.
 5. A DNA sequence according to claim 4 derived from a Caenorhabditis elegans DNA sequence.
 6. A DNA sequence according to claim 3 encoding a functional Δ5-fatty acid desaturase and comprising at least a portion of the sequence shown in SEQ.1 and equivalents to that sequence, or to portions of that sequence, which encode a functional Δ5-fatty acid desaturase by virtue of the degeneracy of the genetic code.
 7. A DNA sequence according to claim 6 derived from a Mortierella alpina DNA sequence.
 8. A DNA sequence according to any one of claims 3 to 7 wherein the DNA sequence is functional in a mammal.
 9. A DNA sequence according to claim 8 in which the DNA sequence is expressed in a mammal
 10. A DNA sequence according to claim 9 wherein the DNA sequence is expressed in a human.
 11. A DNA sequence obtained by modification of a functional natural gene encoding a Δ-5 fatty acid desaturase according to claim 1 or claim
 2. 12. A DNA sequence according to claim 11 wherein the modification includes modification by chemical, physical, or biological means without removing a catalytic activity of the enzyme which it encodes.
 13. A DNA sequence according to claim 12 wherein the modification improves a catalytic activity of the enzyme which it encodes.
 14. A DNA sequence according to claim 12 or 13 wherein the biological modification includes recombinant DNA methods and forced evolution techniques.
 15. A DNA sequence according to claim 14 wherein the forced evolution technique is DNA shuffling.
 16. A polypeptide encoded by a DNA sequence according to any of claims 3 to
 15. 17. A polypeptide according to claim 16 wherein at least a portion of the polypeptide has the sequence shown in SEQ.3 or functional equivalents to that sequence or to portions of that sequence.
 18. A polypeptide according to claim 16 wherein at least a portion of the polypeptide has the sequence shown in SEQ.4 or functional equivalents to that sequence or to portions of that sequence.
 19. A polypeptide according to any of claims 16 to 18 wherein the polypeptide catalyses the conversion of dihomogamma linolenic acid to arachidonic acid.
 20. A polypeptide according to any of claims 16 to 19 wherein the polypeptide has been modified without removing the catalytic activity of the encoded polypeptide.
 21. A polypeptide according to claim 20 wherein the polypeptide has been modified in such a way as to introduce a specific level of saturation of a substrate at a specific location within the molecular structure of the substrate.
 22. A vector containing a DNA sequence or any portion of a DNA sequence according to any of claims 3 to
 15. 23. A method of producing polyunsaturated fatty acids comprising contacting a suitable substrate with a Δ5-fatty acid desaturase according to claim 1 or 2 or a polypeptide according to claim 16 to
 21. 24. A method of converting dihomogamma linolenic acid to arachidonic acid wherein said conversion is catalysed by a Δ5-fatty acid desaturase according to claim 1 or 2 or a polypeptide or modified polypeptide according to any of claims 16 to
 21. 25. An organism engineered to produce high levels of a polypeptide according to any of claims 16 to
 21. 26. An organism engineered to produce high levels of a product of a reaction catalysed by a Δ5-fatty acid desaturase according to claim 1 or 2 or by a polypeptide according to any one of claims 16 to
 21. 27. An organism which has been engineered to carry out the method of claim 23 or claim
 24. 28. An organism according to either of claims 26 and 27 wherein the organism is a microorganism.
 29. An organism according to claim 28 wherein a microorganism is selected from algae, bacteria and fungi.
 30. An organism according to claim 29 wherein a fungi includes phycomycetes.
 31. An organism according to claim 28 wherein said microorganism is a yeast.
 32. An organism according to any of claims 25 to 27 wherein the organism is a plant.
 33. An organism according to claim 32 wherein the plant is selected from oil seed plants and tobacco.
 34. An organism according to claim 33 wherein the oil seed plants are selected from oil seed rape, sunflower, cereals including maize, tobacco, legumes including peanut and soybean, safflower, oil palm, coconut and other palms, cotton, sesame, mustard, linseed, castor, borage and evening primrose.
 35. A seed or other reproductive material derived from an organism according to claim 33 or claim
 34. 36. An organism according to any of claims 25 to 27 wherein the organism is a mammal.
 37. An isolated multienzyme pathway wherein the pathway includes a Δ5 desaturase according to claim 1 or 2 or a polypeptide according to any of claims 16 to 21
 38. A compound produced by a conversion of a substrate, wherein said conversion is catalysed by a Δ5 desaturase according to claim 1 or 2 or by a polypeptide according to any of claims 16 to
 21. 39. An intermediate compound produced by the reaction catalysed by a Δ5 desaturase according to claim 1 or 2 or by a polypeptide according to any of claims 16 to
 21. 40. A foodstuff or dietary supplement containing a polyunsaturated fatty acid produced by a method according to claim 23 or
 24. 41. A pharmaceutical preparation containing a polyunsaturated fatty acid produced by a method according to claim 23 or
 24. 42. Prostaglandins synthesised by a biosynthetic pathway including a catalytic activity of a Δ5 desaturase according to claim 1 or 2 or by a polypeptide according to any of claims 16 to
 21. 43. A method for modulation of prostaglandin synthesis by the control of the levels of expression of a DNA sequence according to any of claims 3 to
 15. 44. A probe comprising all or part of a DNA sequence according to any of claims 3 to 15 or an equivalent RNA sequence.
 45. A diagnostic or search probe comprising all or part of a Δ5 desaturase according to claim 1 or 2 or of a polypeptide according to any of claims 16 to
 21. 46. A method of isolating Δ5 desaturases using a probe according to claim 44 or
 45. 